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Post Construction Water Quality Training: New Regulations

Understanding and Complying with New Water Quality Regulations for Development and Redevelopment Projects

December 6, 2017

Agenda9:15 Check-in / Registration

9:40 Introduction

9:50 Reedy River Water Quality Group Update and Effects on County Requirements

10:20 Context of New Water Quality Regulations

10:50 BREAK

11:05 Modeling Study Results and Implications

11:30 New Water Quality Regulation Roll Out

12:00 LUNCH

12:45 Revisions to the Stormwater Management Design Manual

1:15 Updates from Land Development Staff

2:45 Questions & Answers

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Reedy River – Recent Landmark Events/Regulations

1. 1996 - Colonial Oil pipeline failure

2. 1999 - Lake Greenwood algal bloom

3. 2000 - Greenville County becomes MS4 permittee

4. 2006 - City of Greenville becomes MS4 permittee

5. 2008 - DHEC issues draft nutrient TMDL

6. 2015 - Upstate stakeholders form the RRWQG

Concepts Driving 5R Process

1. Recognize and encourage local watershed restoration efforts

2. Builds partnerships and encourages collaboration

3. Empowers those with a responsibility to reduce loading and decide how WQS will be achieved

4. Acquire practical information for water quality advancements

5. Expedites implementation of watershed restoration

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Bottom-Up5R Approach

Landowners Local Govt Citizens Environmental NGOs Stormwater MS4WRRF

5R Watershed Based Plan

Reedy River Water Quality Group

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RRWQG- Organizational Structure

Watershed Plan Components

1. Description of waterbody and statement of the problems causing the impairment (point and non-point sources)1

Anticipated pollutant load reductions necessary to meet water quality standards2

Water quality restoration activities expected to achieve WQS3

Cost estimates and funding commitments4

Monitoring plan to track effectiveness of restoration activities6

1. Estimated date for achieving WQS7

Anticipated schedule for implementing each activity and expected completion date

5

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Reedy River Water Quality Group

cleanreedy.org

Project Schedule

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RRWQG- Current Status

1. Regular sub-committee and executive committee meetings

2. Public education/outreach, primarily through social media

3. Revised watershed-wide model development

4. On-going monitoring and sampling/data collection

5. Economic impact evaluation

6. BMP implementation and planning

Primary focus on TN with secondary focus on TP…

Context of New Water Quality Regulations

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Why not Nitrogen?

Nitrogen accounts for 78% of the atmosphere making it ubiquitous

It comes to the aquatic ecosystem from everywhere

Wet fall

Dry fall

Point sources

Non-point sources

Surface exchanges

Why Phosphorus?

It is a fundamental element that is essential for life

Limiting nutrient for growth due to excess availability of other constituents

More controllable

An excess amount of phosphorus in aquatic ecosystems could result in eutrophication

Eutrophication could result in excessive production of autotrophs, especially algae and cyanobacteria

The high productivity leads to bacterial activities and high respiration rates, leading to hypoxia and stratification of dissolved oxygen downstream lakes

Low dissolved oxygen causes loss of aquatic life

Degradation of the aquatic life causes further decrease in dissolved oxygen and release of phosphorus which further exacerbates the eutrophication process

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Post Development Standards

EPA’s Stated Goal

Reduce, through regulation, the impacts of new development and redevelopment storm water runoff to the Nation’s waters. –EPA NPDES website

How? “Require completed projects to be designed, built, and maintained so as

to retain the sites’ pre-development hydrologic characteristics to the extent technically feasible” – NRC publication - “Urban StormwaterManagement in the United States”, October 15, 2008

What?

Make the developed site act like it did before it was developed

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Better Good BestNothing

Regulatory Approaches

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EPA Performance Standard Examples

Minimum storm volume to be treated on site (first flush approach)

“…the first one inch of runoff from a 24-hour storm…”

Example: SC Reg. 72-300

Strengths

Simple to calculate

Better than nothing

Weaknesses

No direct connection to pollutants of concern

No accounting of pollutant removal

No incentive to reduce impervious area

Doesn’t allow TMDL restrictions

Oversimplified approach to a complicated problem

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EPA Performance Standard Examples

Minimum storm size to be retained on site

“…the 95th percentile rainfall event…”

Examples: EISA, Beaufort County, SC, State of Maryland, Georgia Blue Book

Strengths

Not complicated to calculate

Incentivizes the reduction of impervious area

Weaknesses

No published 95th percentile rainfall depths

No direct connection to pollutants of concern

No accounting of pollutant removal

Doesn’t allow TMDL restrictions

Oversimplified approach to a complicated problem

Assumes the 95th percentile storm infiltrates in pre-developed conditions for all sites- steep and rocky areas- high groundwater table- clay soils

EPA Performance Standard Examples

Post-development hydrology ≤ pre-development hydrology

“…preserve pre-development runoff conditions for rate, volume, duration, and temperature of discharges for the 1, 2, 10, 25, 50, and 100-year storms…”

Examples: Church Creek watershed in Charleston, SC

Strengths

Acknowledges direct connection between pre-development and post-development hydrologic conditions

Incentivizes the reduction of impervious area

Incentivizes redevelopment

Good flood mitigation approach

Weaknesses

No direct connection to pollutants of concern

No accounting of pollutant removal

Doesn’t allow TMDL restrictions

Ignores pollutants from most storm events because water quality BMPs designed for large storm events do not necessarily work for small storm events

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EPA Performance Standard Examples

Groundwater recharge

“…demonstrate through H&H analysis that the site maintains 100% of the average annual pre-construction groundwater recharge volume…”

Examples: Connecticut and New Jersey

Strengths

Acknowledges direct connection between pre-development and post-development hydrologic conditions

Incentivizes the reduction of impervious area

Promotes groundwater recharge

Weaknesses

No direct connection to pollutants of concern

No accounting of pollutant removal

Nearly impossible to calculate percentage of infiltrated runoff contributing to groundwaterrecharge

Doesn’t allow TMDL restrictions

Promotes recharging the groundwater table with polluted water

Other Approaches

% Removal of Sediment (TSS)

On an annual weight basis

Example: Greenville County

Strengths

Numerically based reduction calculated

Allows for site specific conditions to be taken into account

Allows design characteristics of BMPs to be taken into account

Allows use of Manufactured Treatment Devices(MTDs) in site design

Promotes Low Impact Development (LID) techniques & practices

Weaknesses

No direct connection to other pollutants

Arbitrary reduction of varying loads

Does not incentivize reduction of pollutant generation

Doesn’t allow additional TMDL restrictions

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Other Approaches

Annual loading

Annual loading requirement with predefined BMP removal rates

Examples: Virginia’s Runoff Reduction Method (Chesapeake Bay TMDL), State of NC (Jordan Lake and Falls Lake Rules), Florida’s Harper Method

Strengths

Direct connection to pollutants of concern

Numerically based reduction (spreadsheet)

Weaknesses

Restricts design alternatives

Doesn’t take BMP or individual site characteristics into account

Can’t be used for complex sites

Requires extensive design criteria

Doesn’t allow additional TMDL restrictions

EPA Performance Standard Examples

Post-development POC loading ≤ pre-development POC loading

“…post-construction annual pollutant loads are not allowed to exceed pre-development levels for pollutants of concern…”

Examples: OCRM and SCDHEC Antidegradation Policy, Greenville County (beginning 2018)

Strengths

Deals directly with pollutants of concern

Allows for site specific conditions to be taken into account

Less controversial (policy driven)

Allows design characteristics of BMPs to be taken into account

Overly prescriptive design standards are not needed

Facilitates TMDL restrictions

Weaknesses

More complicated to calculate

More complicated to regulate

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Feasibility Study

Study Method

10 randomly-chosen project sites that were permitted meeting the 85% TSS Trapping Standard or Alternative TSS Standard

Development Type

Greenville County Project Number

Area Disturbed

Area Modeled

Commercial

1307 1.4 1.4

1218 1.6 1.6

1229 1.3 1.3

1276 17.4 17.4

Residential

1296 46.9 81.2

1264 7.9 7.9

1261 47.7 196.5

1288 23.4 23.4

1294 6.2 6.2

Institutional 1231 3.3 3.3

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Study Method

Proposed Standard: no net increase in TP loading from predevelopment conditions

Built pre-development and post-development IDEAL models based on original design submittals

Used incremental modifications, but did not try everything possible. A skilled designer may be able to improve on proposed design modifications.

Level of Difficulty DescriptionNumber of Sites

No Modifications Required

The site met the proposed TP standard as permitted 2 / 10

Minimal Modifications

The existing BMPs were modified by expanding surface area up to 25% or converting to a more effective BMP

2 / 10

Moderate Modifications

At least one additional BMP was required, but that BMP fit within the site footprint and was relatively small

5 / 10

Major ModificationsMore than one additional BMP was required, and/or the additional BMP(s) were relatively large and costly

1 / 10

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PN 1218 (Commercial)

Permitted

New building to replace slightly smaller building

1.55 acres disturbed

Two bioswales (<3% of disturbed area)

Proposed (Moderate)

Added a 50 square foot bioretentioncell (BMPs total <3% of area)

PN 1229 (Commercial)

Permitted

Single building and parking lot

1.3 acres disturbed

Single dry pond (11% of disturbed area)

Proposed (Moderate)

Added 360 sq-ft infiltration trench downstream of pond

Pond size reduced to accommodate infiltration trench w/n property setbacks (BMPs total 11% of area)

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PN 1276 (Commercial)Permitted

Multi-building commercial & office development

17.4 acres disturbed

3 dry ponds, 7 catch basin filter inserts (6% of disturbed area)

Proposed (Major)

2 ponds were converted to BRCs

Added 1,300 sq-ft BRC upstream of 3rd

pond

Proprietary biofiltration units replaced filter inserts in 7 catch basins

1 ac of parking lot was converted to porous pavement (11% including porous pavement)

PN 1307 (Commercial)

Permitted

Single building and parking lot

1.28 acres disturbed

One dry detention pond (12% of disturbed area)

Proposed (Moderate)

Met proposed standard by diverting runoff into 440 sq-ft bioretention cell before planned dry pond (BMPs total 12.5% of area)

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PN 1288 (Residential)

Permitted

37 lot single family subdivision

23.4 acres disturbed

2 VFS and dry pond (3% of disturbed area)

Proposed (No modification)

Met proposed standard with no modifications

PN 1294 (Residential)

Permitted

5 building multifamily development expansion

6.2 acres disturbed

Single dry pond (6% of disturbed area)

Proposed (Minimal)

Pond was unnecessarily deep and was improved by having larger bottom area to promote infiltration (total 6% of area)

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PN 1296 (Residential)

Permitted

212 lot single-family subdivision

47 acres disturbed

Wet pond and 2 VFSs (5% of disturbed area)

Proposed (Minimal)

Converted wet pond to dry pond with impervious forebay section (total 5% of area)

PN 1261 (Residential)

Permitted

128 lot single-family residential subdivision

46 acres disturbed

3 dry detention ponds (1% of disturbed area)

Proposed (No modification)

Met proposed standard with no modifications

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PN 1264 (Residential)

Permitted

40 lot single family subdivision

7.9 acres disturbed

Single dry pond (3% of disturbed area)

Proposed (Moderate)

Added 2,700 sq-ft BRC to grassed area

Dry pond size increased 25% (BMPs total 4% of area)

PN 1231 (Institutional)

Permitted

Single building and parking

3.3 acres disturbed

Part of LCP for detention

Catch basin filter insert (0% of disturbed area)

Proposed (Moderate)

Added 1,200 sq-ft BRC and removed filter insert (1% of area)

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New Water Quality Requirements

Development/ Redevelopment

Location

Development/ Redevelopment Characteristics*

Water Quality Requirement

Any Development in Greenville County < 10,000 sf None**

Sites 10,000 square feet – 0.99 acresOR

other sites meeting criteria for Alternative TSS Standard (as described in Section 9.1.4)

Ensure annual TSS load is≤ 600 pounds per acre

Not within the Reedy River watershed

1 – 25 acresOR

≥ 25 acres and NOT discharging to impaired waterbody (TMDL or 303d)

Trap 85% of annual Total Suspended Solids (TSS) load

≥ 25 acresAND

Discharging to impaired waterbody

Trap 85% of annual TSS loadAND

Anti-degradation Rules for Pollutant of Concern (POC)

Within the Reedy River watershed

1 - 25 acresOR

≥ 25 acres and NOT discharging to impaired waterbody

Trap 85% of annual TSS loadAND

No Increase in Annual Loading for Total Phosphorus (TP)

≥ 25 acresAND

Discharging to impaired waterbody

Trap 85% of annual TSS loadAND

Anti-degradation Rules for TP and POC

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https://gis.dhec.sc.gov/water/Stormwater.html

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Calculations

Make separate pre-development and post-development models

Compare load at outlet from each model

Model same area in both models (IDEAL now reports total project area at outlet)

Offsite drainage does not have to be subtracted out since it won’t change

IDEAL Output Report

Pre-development Post-development

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Revisions to Design Manual

https://www.greenvillecounty.org/LandDevelopment/DesignManual.aspx

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Chapter 3: Plan Submittal

Updated section on flood control requirements for submittals

References newer County Floodplain Ordinance

Updated list of approved software

Chapter 9: Water Quality

Complete re-write

Removed unnecessary methods for calculating water quality compliance

New Outline:

Requirements (starting with Table 9-1)

Tools for Compliance

Water Quality Background and Loading

Water Quality Pollutant Removal Mechanics

Constructed Water Quality Controls

Additional Water Quality Controls (non-structural design techniques)

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Chapter 9: Water Quality

Added section on infiltration testing requirements for BMPs relying on infiltration

Chapter 10: Low Impact Development

Complete re-write; used to be an extension of Ch. 9

High-level guidance for using LID strategies to meet water quality requirements during each stage of design process

From 2013 Chapter 10:

LID is the “new normal”

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Appendix F: During Construction EPSC Specs & Details

Minor changes resulting from 2015 Construction BMP Audit

SC-03 Silt Fence

SC-06 Construction Entrance

Appendix F: During Construction EPSC Specs & Details

SC-07B Inlet Filter Type B

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Appendix G: Post Construction WQ Suggested Uses Placed former Table 10-4 in this appendix

Updated to include all BMPs

Quick-reference for BMP selection and major requirements

Relative maintenance needs

Relative cost

Drainage area

Soils

Minimum size

Slope

Water table/bedrock clearance

Setback

Maximum depth

Appendix H: Post Construction WQ Specs & Details

Pulled all BMP Specs & Details into one Appendix

Minor changes to some BMPs

Added section to each to explain how to model in IDEAL

Added two new BMPs

Rain Garden

Regenerative Stormwater Conveyance

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Rain Garden

Rain Garden

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Regenerative Stormwater Conveyance

Regenerative Stormwater Conveyance

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LDD Updates

Contact Info

For Design Manual and permitting questions:

GC Land Development Division: 864-467-4610

For IDEAL software installation questions:

Becca Coulter: 803-214-5914

For IDEAL modeling questions:

John Schooler: 757-549-5352